High-voltage metal-oxide-semiconductor (HVMOS) devices are widely used in many electrical devices, such as CPU power supplies, power management systems, AC/DC converters, etc.
There are a variety of forms of HVMOS devices. A symmetric HVMOS device may have a symmetric structure on the source side and drain side. High voltage can be applied on both the drain and source sides. An asymmetric HVMOS device may have asymmetric structures on the source side and drain side. For example, only one of the source side and drain side, typically the drain side, is designed for sustaining high voltages.
HVMOS devices may need to undertake a biased-temperature stress (BTS) test, during which a high voltage is applied on the gate to stress the device at an elevated temperature. It has been found that if a symmetric HVNMOS is stress-tested under a high gate-voltage, the leakage current between the drain region and source region significantly increases compared to the leakage current before the BTS stress test. The off-state leakage current can be three to five orders higher than before the BTS stress test. Thereafter, the leakage current stays high even after the BTS stress voltage is removed.
Therefore, a solution for eliminating the effects of the BTS test is needed.